In many fields of industry, e.g., chemical/pharmaceutical manufacturing, food processing, metallurgy/materials engineering, etc., it is often necessary to blend several materials to attain some desired mixture. It may be necessary to monitor the properties of the mixture during blending to verify that the blending process is proceeding as planned. In some cases, it may be desirable to monitor changes in composition, phase, or other properties of the materials in the mixture, as can often occur where the mixture is reactive, or where it is heated or otherwise acted upon during blending. In other cases, it may simply be desirable to monitor the properties of the mixture during blending to confirm the degree of blending. As an example, pharmaceuticals are often prepared by blending very precise amounts of different materials until they are very uniformly and completely mixed, and to control time and costs, it is desirable to cease blending as soon as mixing appears to be sufficiently thorough. Further, blending can be quite time-consuming because it must often occur without the use of rotating impellers/vanes or other mechanical mixing aids in the mixing bin, since such structures can shear the mixture and cause undesirable changes in its properties. As a result, the materials being mixed might only be mixable by tumbling them in a mixing bin, with the mixing bin having sufficient free space (and a suitable tumbling speed) that the materials uniformly commingle over time as blending proceeds.
Molecular spectrometers are sometimes used to monitor the characteristics of the mixture, but spectrometric measurements can be difficult to obtain from one of the aforementioned mixing bins. Most spectrometers function by emitting reference light having known wavelength(s) and intensity into a window in the mixing bin, and then capturing the light scattered from (and/or transmitted through) the mixture, with the difference between the reference and measured light providing information regarding the characteristics of the mixture. However, where materials are tumbled in a mixing bin, the composition adjacent the window can constantly change: at one moment it may be a solid or liquid mixture which has fallen or splashed against the window, and at another moment it may be the air or other gas that occupies the free space within the bin. Since one generally wishes to know the characteristics of the mixture, not the free space, one is then left with the issue of when to take spectrometric readings: readings should be actuated, or should be observed, when the mixture falls against the bin window. But since the time at which the mixture falls against the window can vary depending on a number of factors—such as the caking/agglomeration (or viscosity/surface tension) of the mixture, the shape of the mixing bin, the volume of the mixture versus the volume of the free space, the rotational speed of the mixing bin, etc.—it can be difficult to determine when to actuate or observe spectrometric readings. This can in turn lead to less than optimal results in the measurement of mixture properties.